Ignition system



Oct. 22, 1968 Y J. L. SHIELDS 3,

IGNITION SYSTEM Filed June 7, 1966 o lllll|||- INVENTOR JAMES L. SHIELDSUnited States Patent 3,406,671 IGNITION SYSTEM James L. Shields, Linton,Ind., assignor t0 Luvals, Inc., Linton, lnd., a corporation of IndianaFiled June 7, 1966, Ser. No. 555,852 5 Claims. (Cl. 123-148) ABSTRACT OFTHE DISCLOSURE An ignition system for internal combustion engines whichprovides a hotter spark of shorter duration than that provided bystandard ignition systems is disclosed. The self-induced (flyback)voltage of the primary winding of the ignition coil is utilized to drivethe base electrode of a transistor positive with respect to the emitterelectrode when the breaker points of the system open. The base electrodeand the collector electrode of the transistor are both connected toground potential when the ignition breaker points are closed, causingfull conduction of the transistor and minimizing transistor junctiontemperature This invention relates to ignition system for igniting thecombustible mixture of an internal combustion engine and moreparticularly to ignition systems wherein a semiconductor, such as atransistor, is used to control the current flow through the primarywinding of an ignition coil.

The invention is applicable to generally known and used ignition systemsof the kind in which a pair of breaker points control a supply ofcurrent from a battery to the primary winding of an ignition coil andthe points are opened and closed to sequentially interrupt and connectthe current supply whereupon a high voltage generated in the secondarywinding of the coil is applied to a distributor system operatedsynchronously with the breaker points. The distributor system includessparkplugs which initiate combustion of the fuel supplied to carcylinders of the engine with which the spark-plugs are associated.

One object of this invention is to provide an ignition system which willprovide a spark which is hotter but of shorter duration than thatprovided by ignition systems now in general use, and thereby increasethe useful life of the points and spark-plugs associated with thesystem.

It is an object of this invention to provide an improved ignitionsystem, of the type described, wherein the self induced (flyback)voltage of the primary winding of the ignition coil is utilized to drivethe base electrode of a transistor positive with respect to the emitterelectrode when the breaker points of the system open, thus causing anextremely sharp cut-off of conduction of the transistor, and a resultinghigh voltage in the secondary winding of the ignition coil.

Another object of this invention is to provide a transistor controlledignition system wherein the collector electrode of the transistor isconnected directly to the ground side of the system thereby eliminatinginsulated mounting of the transistor and consequently providing betterheat dissipation and ease of installation.

A further object of this invention is to provide a transistor controlledignition system wherein the transistor base-to-ground current aids theemitter-to-collector current in causing maximum current to flow throughthe primary winding of the ignition coil during the conduction cycle ofthe transistor.

Another object of this invention is to provide a transistor controlledignition system wherein the transistor base electrode is at the sameelectrical potential as the collector electrode during the time that theignition breaker points are closed, thus causing full conduction of thetran- 3,406,671 Patented Oct. 22, 1968 sistor and minimizing the rise intransistor junction temperature.

Another object of this invention is to provide a transistor controlledignition system wherein the complete electronic controls can be attachedto an ignition coil and the assembly thus made directly interchangedwith an automobiles original ignition coil, thus eliminating therequirement for additional mounting holes, sub-chassis, heat sinks andwiring.

A further objective of this invention is to provide a transistorignition system wherein the transistor is caused to alternately go fromfull conduction to full cut off during the respective closed and openconditions of the ignition systems breaker points, thus minimizing therise in transistor junction temperature, and eliminating transistorthermal runaway.

One form of the invention is illustrated in the accompanying drawing.

Referring to the drawing, the reference numeral 20 designates a sourceof electrical power (normally a six volt storage battery) on a motorvehicle. One side of the storage battery 20 is connected directly toground 42, as is shown, and the other side is connected to an ignitionswitch 22. The other side of the ignition switch 22 is connected to oneside of the primary winding 24 of the ignition coil 26. The ignitioncoil illustrated is a standard type with a low impedance primary windingranging from 0.5 to 1.5 millihenrys and with turn ratios of 250 to 1 to400 to 1.

The ignition system of this invention includes a semiconductor such as atransistor 28 having an emitter electrode 30, a base electrode 32 and acollector electrode 34. Suitable transistors include those designated2N174, 2Nl90, 2N2152 and others of similar characteristics and powerratings. The emitter electrode 30 is connected directly to the junction36. The base electrode 32 is connected to junction 38 via junction 54and the resistor 40 having a value of to 500 ohms. The collector 34 ofthe transistor 28 is connected directly to the ground 42 side of thesystem. A rectifier diode 44 is connected between the junctions 36 and38 and a capacitor 46 having a value of 0.1 mfd. -20% at 400 WVDC. isconnected between the junction 38 and the ground 42. A suitablerectifier diode 44 is the type commercially designated IN1692.

One side of the secondary winding 48 of the ignition coil 26 isconnected to the junction 50 and the other side of the secondary Winding48 is connected to the center junction 60 of the ignition systemsdistributor cap. It should be noted that the secondary winding 48 of theignition coil 26 is inductively coupled to the primary winding 24 andthat one side of each winding is common to the junction '50.

Reference numeral 52 indicates a set of breaker points of which one sideis connected directly to the base electrode 32 of the transistor 28 viathe junction 54. The other side of the breaker points 52 is connecteddirectly to ground 42 of the system. Opening and closing of the breakerpoints 52 are in synchronism with the operation of the engine, as is therotation of the rotor contact 56. Thus the rotor contact 56 is orientedin such a manner that the ignition spark, which occurs when the breakerpoints 52 open, is distributed in sequence to the proper spark plug 58to cause ignition of the combustible mixture within the respectivecylinder of the engine.

It will be appreciated that the referenced drawing illustrates atransistor ignition system of the type described as applied to a fourcylinder engine. It will also be appreciated that a transistor ignitionsystem of the type described is applicable to internal combustionengines having less or more than four cylinders.

In operation of this system, when the engine is being cranked thebreaker points 52 are caused to open and close by the cam action of theengines distributor camshaft. With the ignition switch 22 closed and thebreaker points 52 closed, the base electrode 32 is connected directly toground 42. Thus the transistor 28 is'biased for optimum currentcondition from emitter to collector which causes maximum current to flowfrom the battery through the primary winding 24 of the ignition coil 26to ground 42 via the transistors emitter electrode 30 and collectorelectrode 34.

It is important to observe that the small base current (which ischaracteristic of all transistors) is utilized in this invention to aid,instead of shunt, the current flow in the primary winding of theignition coil. It is also important to observe that under this conditionof operation there is no resistance between the base electrode 32 andthe ground connection 42. Thus, there is no difference in the voltagepotential of the base electrode 32 and the collector electrode 34.Hence, the voltage drop between the emitter electrode 30 and thecollector electrode 34 is at a minimum. By this arrangement it is seenthat the operating temperature of the transistor 28 is maintained at avery low level.

When the breaker points 52 open, the base electrode 32 of the transistor28 is no longer connected to ground thus the electrical potential of thejunction 38 (which is positive with respect to the emitter electrode 30)is applied to the base electrode 32 via the resistor thus causing sharpconduction cut-off of the transistor 28. The sharp conduction cut-01f ofthe transistor 28 causes a sharp cut-otf of current flow through theprimary Winding 24 of the ignition coil 26. The resulting high voltagewhich is induced in the secondary winding 48 of the ignition coil 26 isapplied to the proper spark plug 5 8 vi the junction 60, the rotorcontact 56, and a junction 62, thus causing ignition of the combustiblemixture within the respective cylinder of the engine. At the same timethat the induced high voltage occurs in the secondary Winding 48 of theignition coil 26, a self induced voltage occurs in the primary winding24. This voltage, which is of a considerably higher potential than thatof the storage battery 20, is applied to the capacitor 46 via the diode44 thus establishing a positive voltage potential at the junction 38.This voltage is applied to the base electrode 32 via the resistor 40 andthus maintains conduction cut-01f of the transistor 28 while the breakerpoints 52 are open. When the breaker points 52 close, the junction 54and hence the base electrode 32 are connected to the ground 42 and thepositive voltage at the junction 38 is dropped across the resistor 40. Avoltage of the proper polarity and magnitude at the junction 38, is thusmaintained, to cause sharp conduction cut-off of the transistor 28 whenapplied to the base electrode 32 via the resistor 40 as will be thecondition when the breaker points 52 are again caused to open.

The embodiments of this invention, as specifically disclosed herein,constitute presently pretered forms, and it is to be understood that theinvention is not limited to the specific disclosure or by the value ofthe various components which are mentioned in the disclosure solely forthe purpose of describing one complete and operable form of theinvention; but that the nature of the invention is indicated in theobjectives set forth above and is particularly and distinctively claimedhereinafter.

What I claim as my invention is:

1. In an ignition system for internal combustion engines of the kind inwhich a pair of breaker points control a supply of current from abattery to the primary winding of an ignition coil and are opened andclosed to sequentially interrupt and connect the current supplywhereupon a voltage generated in the secondary winding of the ignitioncoil is applied to a distributor system operated synchronously with thebreaker points: a transistor having its emitter elemtrode connected tothe primary Winding of said ignition coil, and the collector electrodeof the transistor and one of the breaker points being connected to thesame potential level, the other breaker point being connected directlyto the base electrode of the transistor, and a circuit connecting saidprimary winding and said other breaker point in parallel with saidtransistor, said circuit containing current limiting means and diodemeans to prevent reverse current flow therethrough, whereby current flowthrough the transistor commences immediately and remains at a high levelupon closing of the breaker points without causing an undesirabletemperature rise in the transistor.

2. The improvements in an ignition system as claimed in claim 1 in whichthe potential level is ground.

3. The improvement in an ignition system as claimed in claim 1 havingcircuit means connecting the primary winding of the ignition coil tosaid base electrode for applying the self-induced flyback voltage in theprimary winding of the ignition coil upon opening of the breaker pointsto said base electrode, whereby current flow through the transistor iscut-off sharply to produce high voltage in the secondary winding of theignition coil.

4. The improvement in an ignition system as claimed in claim 3 in whichsaid circuit means includes a capacitor-resistance network and arectifier connected between said capacitor and said primary winding,whereby the cut-off of the current flow through the transistor uponopening of the breaker points is maintained during the entire time thebreaker points remain open and the transistor is switched from fullconduction to beyond conduction cut-off upon closing and opening,respectively, of said breaker points.

5. An ignition system wherein the primary circuit is directly connectedwith a source of electronic potential, and by transistor controlledswitching from this source to ground potential through an emittercollector circuit of the transistor switching, a parallel connectedswitching circuit from primary to ground through engine driven breakerpoints, means directly connecting the base of the transistor switchingwith ground through said breaker points, a current limiting means in theparallel switching circuit, a diode poled to prevent current reverseflow between the switching circuits, and capacitor means connected to becharged by current flow from the primary through the diode when theswitching circuits open and connected to reverse bias the base emittercircuit of the transistor switching through the parallel connectedswitching circuit while this circuit is open and then discharge when thebreaker points close.

References Cited UNITED STATES PATENTS LAURENCE M. GOODRIDGE, PrimaryExaminer.

